The present invention relates to an apparatus for making a hollow workpiece. More particularly this invention concerns an apparatus for pressurizing a space between two plates to deform them outwardly away from each other into a hollow workpiece.
It is known to make a hollow workpiece by welding together the peripheries of two plates and forming one of them adjacent the periphery with a small throughgoing feed hole. The two plates are clamped at their peripheries between edge regions of a pair of die halves forming a cavity conforming to the outside shape of the workpiece to be produced. A fluid under very high pressure is introduced into the space between the plates through the feed hole to push the plates apart against the inside faces of the respective halves of the die cavity, thereby plastically deforming the plates and imparting to them the exact shape of the cavity. The resultant workpiece has an exactly determined outside shape and a smooth interior.
The problem with these systems is that, as the plates are being expanded transversely to their main dimension, they inherently creep somewhat parallel to this main dimension, that is perpendicular to the direction in which the two die halves are pressed together. Thus the feed hole, even when the periphery is solidly clamped, will move somewhat if only because of plastic deformation of the plate it is formed in. The result can be misalignment of the feed hole with the feed passage used to force fluid in between the plates. If the feed hole and/or feed passage are made big enough to accommodate this movement, other problems like leakage are created.
Accordingly German document 198 16 566 of S. Schwarz et al describes a system where the feed passage is provided in a slide that can move somewhat parallel to plates. Thus as the plate periphery creeps inward, the slide can move inward with it to maintain alignment of the feed passage in the slide with the feed hole in the plate.
This system has several disadvantages. It creates a substantial leak problem between the slide and the die parts. The slide must be able to move freely to follow the workpiece creep, but at the high pressures being employed this can be difficult so that the slide will stick and become misaligned. Finally it is necessary to provide a flexible coupling to the movable slide, creating a weak spot in a system employing very high pressure.
It is therefore an object of the present invention to provide an improved system for making a hollow workpiece from two plates by internal high-pressure deformation.
Another object is the provision of such an improved system for making a hollow workpiece from two plates by internal high-pressure deformation which overcomes the above-given disadvantages, that is which allows the plates to creep in a system that is sure to maintain alignment of the feed passage with the feed hole without leakage.
A further object is to provide such a system where no flexible connection need be made to the movable die part.
An apparatus for forming two plates into a hollow workpiece has according to the invention a pair of dies together forming a cavity and having edge regions adapted to be pressed together in a direction against outer peripheries of the plates. An outer element in the edge region of one of the dies is adapted to rotate therein about an axis generally parallel to the direction and an inner element set in the outer element is rotatable therein about an axis generally parallel to and offset from the outer-element axis. The inner element is formed offset from the respective inner-element axis with an axially throughgoing feed passage aligned with a feed hole in the plate engaging the one die. A fluid is forced under pressure through the passage and hole into a space between the plates to deform the plates away from each other in the direction while displacing the hole perpendicular to the direction with rotation of the outer element in one sense and rotation of the inner element in an opposite sense for movement of the passage in a straight line perpendicular to the direction.
With this system therefore the two elements rotate in the one die, which can be the upper or lower die, so that sealing between them and between the outer element and the one die is very simple. At the same time the two elements can rotate smoothly so that the passage of the inner die can follow the straight-line movement of the hole in the one plate as same creeps inward during the main deformation phase of the shaping operation.
According to the invention the two elements are disks of substantially circular shape. They have outer peripheries or surfaces that are at least partially frustoconical so that they will not shift substantially parallel to the direction toward the plates no matter how much pressure is employed.
The inner-element disk has a diameter equal to at most half a diameter of the outer-element disk. In addition the inner element has a face engageable with the one plate and formed around the passage with a collar engaging in the hole and fitting the inner element to the hole. This collar can be tapered toward the plates to fit snugly in and form a good seal with the hole of the one plate.
The inner element and the one plate have confronting faces. Another passage formed in the one plate opens at the one-plate face in alignment with the inner-element passage. Furthermore the one-plate face is formed with an enlarged recess into which the one-plate passage opens. The inner-element passage opens into the recess. This recess is circular, generally centered on the outer-element axis, and of a diameter smaller than a diameter of the outer element.